Palmer, 38, is leaving the game after 14 seasons, including the last five in Arizona.

“Over the years, I’ve had teammates who decided to hang it up and I would ask them how they knew it was time to walk away,” Palmer wrote in an open letter posted on the Cardinals website. “The answer was almost always the same: You just know.

“For me that time is now. Why? Quite simply, I just know.”

Palmer led the Cardinals to a 3-4 record to start the 2017 season before breaking his left, non-throwing arm in Week 7 against the Rams and going on injured reserve days later.

The 2003 No. 1 overall pick out of the University of Southern California played eight seasons with the Bengals followed by a short, two-year stint in Oakland. Traded to Arizona in 2013, Palmer then led the Cardinals to two straight playoff appearances from 2014-15, including a loss in the NFC Championship in the latter season.

“In the end, it’s not what happens on the football field that sticks with you. Those are details that I know fade with time,” he wrote.

“Now it’s time for something else and I’m excited to find out exactly what that will be. I know for sure it will center around the five most important people in my life — my wife Shae and our four awesome kids. They have sacrificed so much to let me pursue my football goals. Now it’s their turn. We can only hope that the next chapters are as rewarding and provide as much joy as the last 15 years in the NFL have.”

Palmer ends his career 12th on the all-time rankings with 294 touchdown passes.